Citroen C5 2002 ABS sensor lights up after 50 yards

JesseJames_2

Car failed the MOT due to this.

After about 50 yards the ABS sensor light comes on, and stays on.
It is OK if you start the engine and keep it ticking over, it does not come on - it only comes on when the car is moving.

Previously, last summer I changed a suspension cylinder, and while waiting for the replacement, changed the back brake disc and pads. (just the 1 wheel, same side as suspension)

As soon as the suspension was fixed and car put back on the road the light came on after about 50 yards and has been the same since.

So, I reckon, I must have done something to upset the sensor on the back wheel, or damaged the sensor cable (as it runs near the suspension cylinder), but the cable seems fine and not damaged.

If I remember correctly, the back disc took a bit to get off, and I'm sure I gave it a wee bit hammering to get it off.

Any ideas what I should check for.
I'm thinking of getting the sensor cable for a start, but what about within the wheel itself?

The yellow warning light is the same one as here...
http://forumbilder.se/CF7M3/imag0102.jpg

SuperAllyB

Not a mechanic, but could it be to do with uneven brakes on each side?

Marktheshark

Did you use the right discs, some of the older ABS had groves in the disk which the sensor reads.
The cheapo budget disks dont have the groves.

Strider590

Citroen/Peugoet, all the same, all sh*te

But I had a 306, the ABS light came on, turned out to be a VERY common fault where the ABS ring (which is basically like a small metal ladder around the hub, just behind the brake disc) had snapped. Got someone to weld it back together and problem solved.... You can also buy them for under £5, but fitting requires removing the hub.

facade

As the problem started after you messed with it, it is most likely something that you did.

I agree with Mark & Strider, start by examining the new disc to see if the sensor ring is present. You should be able to see what the sensor points at with the disc off.

If the wire or sensor was broken, I'd expect the light to stay on not go out and come back after 50 yards.

BeenThroughItAll

Just one point that's not been made here as far as I can see, but did you really mean you replaced disc and pads on only one side of the car?


That's just madness and false economy.

AdrianC

The ABS computer does a self-test of the sensor on start-up, checking resistance and continuity. It's passing that.

It then monitors the signal compared to the other three wheels at all times whilst the car's moving - and that's what it's failing. So, yes, the ring is a possibility.

JesseJames_2

Firstly, I still have the old disc and it was identical to the new one (apart from wear). I do not see any 'grooves' as such.

Second, is the sensor ring easily visible with the disc off?
That could be a good candidate for the problem.

Strider, was your ABS light permanently on, or same as mine and came on after 50 yards or so?

OnanTheBarbarian

I would imagine you would need to remove the ABS pulse sensor from the hub to see if the ring is visible, but I have no experience of these cars (only on BMW's). They are sometimes a pig to remove once the allen bolt has been undone (make sure you get the allen key firmly pressed into the bolt head to avoid rounding it off and giving you a whole world of additional pain)

Your light only comes on after you start moving as it only reads a pulse from the rings rotating, so when stationary it doesn't know if there is a ring present or not. When you move it is getting a signal from 3 of the 4 sensors, so throws up the fault light.

Strider590

The ABS ring I mentioned should be easy to see if you turn the steering wheel fully, jack the car and remove the road wheels.

The other to be aware of, is that copper slip gets used a lot when doing brake work, the mechanic might have accidentally got some on the ABS sensor (hall sensor) which would completely screw it up.

s_b

dont know if on this car the abs pickup is a sensor bolted into the hub or is part of the wheel bearing
i would stab at it being bolted in and its highly likely on working on one of the hubs you broked it
a scan with an appropiate abs enabled tool would be able to locate which one is broken rather than guessing an getting it wrong so it might be wise to take car to a garage knowledgeable on citroens with the gear in to scan it